1. Field of the Invention
The present invention relates to a module for optical devices, which comprises a solid-state image pickup element and an optical path defining unit for defining an optical path to an effective pixel area formed in one surface of the solid-state image pickup element, and also relates to a manufacturing method of the module for optical devices.
2. Description of Related Art
In recent years, modules for optical devices, which are to be incorporated into optical devices such as digital cameras and mobile phones with camera functions, have been developed (see, for example, Japanese Patent Application Laid Open No. 2002-182270).
FIG. 1 is a cross sectional view showing the structure of a conventional module for optical devices. In FIG. 1, the reference numeral 30 represents a wiring substrate, and a pattern of conductor wiring 31 is formed on both surfaces of the wiring substrate 30. The conductor wirings 31 formed on both surfaces of the wiring substrate 30 are suitably connected to each other in the wiring substrate 30. A DSP (digital signal processor) 32 is bonded (die-bonded) onto the wiring substrate 30. A spacer 33 that is a sheet of insulating adhesive is bonded onto the flat surface of the DSP 32, and a solid-state image pickup element 34 is bonded onto the spacer 33. Each connection terminal of the DSP 32 is electrically connected to the conductor wiring 31 by a bonding wire 32w, and each connection terminal of the solid-state image pickup element 34 is electrically connected to the conductor wiring 31 by a bonding wire 34w. 
A cylindrical lens holder body 35 has a focus adjuster 36 that holds a lens 37 inside one end, and the other end of the lens holder body 35 is bonded to one surface of the wiring substrate 30. Bonded between the lens 37 in the lens holder body 35 and the solid-state image pickup element 34 is an optical filter 38 to which a filter treatment for cutting infrared rays among the incident rays was applied. The focus adjuster 36 is screw-fitted into the lens holder body 35, and the position of the focus adjuster 36 with respect to the lens holder body 35 is changed by turning the focus adjuster 36. By using the one surface of the wiring substrate 30 to which the lens holder body 35 is bonded as the basis, the position of the lens 37 is determined by the lens holder body 35 and focus adjuster 36 (hereinafter referred to as the lens holder).
The size (particularly a dimension in the thickness direction) of the wiring substrate 30 of the module for optical devices is within the specification values. However, the wiring substrate 30 is curved, warped, or the like due to manufacturing irregularities. Moreover, even after the lens holder body 35 is bonded, the wiring substrate 30 is still warped, curved, etc. In other words, when positioning the lens 37, there is a possibility that the optical length from the lens 37 to the solid-state image pickup element 34 may not agree with the focal length f of the lens 37 due to the warp and curve of the wiring substrate 30 functioning as the positioning basis.
FIG. 2 through FIG. 4 are explanatory views showing the problems of the conventional module for optical devices, and each figure shows a cross section of the module for optical devices.
FIG. 2 shows a state of the wiring substrate 30 in which the center portion is raised. The lens 37, the center portion of the wiring substrate 30 and the solid-state image pickup element 34 disposed on the center portion of the wiring substrate 30 are kept parallel to each other, but since both ends of the wiring substrate 30 are lower than the center, the lens holder body 35 bonded to the wiring substrate 30 is in a state of being moved down relative to the center portion of the wiring substrate 30. In short, the basis of positioning the lens 37 is moved down. Consequently, the optical length between the lens 37 and the solid-state image pickup element 34 differs from the focal length f of the lens 37, and becomes f−Δf (Δf is the deformation in the thickness direction of the wiring substrate 30).
In such a case, in order to make the optical length between the lens 37 and the solid-state image pickup element 34 equal to the focal length f of the lens 37, the optical length between the lens 37 and the solid-state image pickup element 34 is adjusted to the focal length f of the lens 37 by turning the focus adjuster 36. In other words, an adjustment corresponding to the deformation Δf is made by the focus adjuster 36 so as to locate the solid-state image pickup element 34 at the position of the focal length f of the lens 37.
FIG. 3 shows a state of the wiring substrate 30 in which the center portion is depressed. The lens 37, the center portion of the wiring substrate 30 and the solid-state image pickup element 34 are kept parallel to each other, but since both ends of the wiring substrate 30 are higher than the center, the lens holder body 35 bonded to the wiring substrate 30 is in a state of being moved up relative to the center portion of the wiring substrate 30. In short, the basis of positioning the lens 37 is moved up. Consequently, the optical length between the lens 37 and the solid-state image pickup element 34 differs from the focal length f of the lens 37, and becomes f+Δf (Δf is the deformation in the thickness direction of the wiring substrate 30). Therefore, it is necessary to make an adjustment corresponding to the deformation Δf by the focus adjuster 36, and adjust the solid-state image pickup element 34 to the position of the focal length f of the lens 37.
As described above, in the conventional module for optical devices, since the lens holder body 35 is bonded to the wiring substrate 30 by using the wiring substrate 30 as the basis of positioning the lens 37, the optical length between the lens 37 and the solid-state image pickup element 34 sometimes differs from the focal length f of the lens 37 due to irregularities such as the warp or curve of the wiring substrate 30.
As a result, for each module for optical devices, it is necessary to perform an adjustment process for adjusting the optical length between the lens 37 and the solid-state image pickup element 34 to the focal length f of the lens 37, and an expensive facility and a worker are required for the adjustment. Moreover, a skilled worker is required for the adjustment. Further, two mechanical parts, namely the lens holder body 35 and the focus adjuster 36, are necessary as a lens holder, and it is structurally difficult to reduce the size of the lens holder and the size of the module for optical devices. Besides, since the lens holder is a mechanical component, mass production is difficult, and the ratio of the cost of producing the lens holder to the cost of producing the module for optical devices is high, and consequently the production cost is increased.
On the other hand, FIG. 4 shows a case where the plate thickness of the wiring substrate 30 varies depending on locations. As shown in FIG. 4, even when the wiring substrate 30 has different thicknesses at the left and right ends such that the wiring substrate 30 has a thick plate thickness at the right end and a thin plate thickness at the left end, for example, if the wiring substrate 30 has a rectangular shape with a thickness of around 10 mm and the thickness difference between both ends of the wiring substrate 30 is around ±0.01 mm, the plate thickness of the wiring substrate 30 is within the standards.
However, when the lens holder body 35 is bonded to the wiring substrate 30, the lens holder is fixed in a tilted state with respect to the wiring substrate 30 and solid-state image pickup element 34. As a result, the optical axis of the lens 37 and the perpendicular axis of the solid-state image pickup element 34 have a difference of angle θ, and the solid-state image pickup element 34 can not accurately receive incident light passing through the lens 37. In other words, it is impossible to accurately project the image of an object onto the solid-state image pickup element 34.
Further, in the conventional module for optical devices, each connection terminal of the DSP 32 and each connection terminal of the solid-state image pickup element 34 are electrically connected to the conductor wire 31 by the bonding wire 32w and the bonding wire 34w. Therefore, it is necessary to provide a space for the bonding wire 32w, the bonding wire 34w, and the conductor wiring 31 connected to these wires.
More specifically, it is necessary to provide a space capable of wiring the bonding wire 32w and the bonding wire 34w between the DSP 32 and the solid-state image pickup element 34, and between the solid-state image pickup element 34 and an optical filter 38, and it is also necessary to provide a space capable of placing the conductor wiring 31 on the periphery of the DSP 32 and the solid-state image pickup element 34 on the wiring substrate 30. Consequently, the size of the module for optical devices, for example, distance A between an end of the solid-sate image pickup element 34 and the inner wall of the lens holder body 35 is increased, resulting in the large-sized module for optical devices.